1. Field of the Invention
The present invention relates to a traction control device for a vehicle.
2. Description of the Related Art
In a known engine, when the engine is accelerated, the occurrence of slippage of the driven wheel is detected by the difference between the speed of rotation of the free running wheel and the speed of rotation of the driven wheel, and when slippage of the driven wheel occurs, the output torque of the engine is reduced by stopping the supply of fuel fed to some of the engine cylinders (see Japanese Unexamined Patent Publication No. 58-8436). In this engine, the number of the engine cylinders in which the supply of fuel is stopped is increased as the slippage of the driven wheel becomes greater, and thus the output torque of the engine is controlled in accordance with the severity of the slippage.
However, when the severity of the slippage fluctuates within a relatively short time, the number of engine cylinders in which the supply of fuel is stopped fluctuates within a relatively short time, and accordingly, the supply of fuel and the prohibition of the supply of fuel to the engine cylinders are alternatively repeated at a high frequency.
When the prohibition of the supply of fuel for the engine cylinder is started, fuel accumulated on the inner wall of an intake manifold gradually flows into the engine cylinders in which the supply of fuel is stopped. Therefore, when the supply of fuel and prohibition of the supply of fuel to the cylinders are alternatively repeated at a high frequency, a large amount of unburned HC is discharged into the exhaust passage. Furthermore, if the supply of fuel for the engine cylinder is prohibited, a large amount of oxygen is discharged into the exhaust passage from the engine cylinders, and consequently, since a large amount of unburned HC is burned in the exhaust passage, a problem arises in that parts of the exhaust system, for example, the catalyst, are damaged due to the heat from the burning of the unburned HC.
In addition, where the supply of fuel and prohibition of the supply of fuel to the cylinders are alternatively repeated at a high frequency, when the supply of fuel for the engine cylinder is started, since a large amount of fuel adheres to an intake port, the amount of fuel fed into the cylinder in which the supply of fuel is started is small. Therefore, the burning time becomes long and continues until next intake stroke in the cylinder. Consequently, when the intake valve is opened, the burning gas flows back to the intake manifold, and thus a problem arises in that an air-fuel mixture in an intake pipe is ignited and burned, i.e., a backfire occurs.